1. Field of the Invention
The present invention relates to a flow-path exchanging valve and more particularly to a three-way valve or four-way valve which is equipped with a stopper pipe for a valve element and is used in a heat pump system.
2. Description of the Prior Art
A previously known typical example of the rotary flow path exchanging valve is a four-way valve or three-way valve comprises a cylindrical valve housing, a valve element rotatably attached to the valve housing, a valve seat plate and an electromagnetic actuator. The valve seat plate includes a low pressure port secured to the valve housing and connected to a low-pressure conduit, a high pressure port secured to a high pressure conduit and at least one exchanging port. The valve element is brought into contact with the valve seat plate at its end surface and rotates between a first rotary position and a second rotary position so that said exchanging port is selectively communicated with either one of said low pressure port and said high pressure port.
The rotary flow-path exchanging valve includes a high pressure communicating groove for communicating the high pressure port formed in the valve element with the exchanging port and a low pressure communicating groove for communicating the low pressure port with the exchanging port. A stopper pipe is secured to the high pressure port or low pressure port of the valve seat plate. The stopper pipe protrudes into the high pressure communicating groove or the low pressure communicating groove. The stopper pipe abuts on the side wall of the high pressure communicating groove or low pressure communicating groove to limit the rotary range of the valve element between the first rotary position and second rotary position in a door-stop manner. Thus, a first exchanging state, in which the exchanging port is communicated with the high pressure port, and a second exchanging state, in which the exchanging port is communicated with the low pressure port, are established correctly. The above rotary flow-path exchanging valve has the following disadvantages. When the stopper pipe is heated at a high temperature to solder the stopper pipe to the high pressure port of the valve seat plate, the material of the stopper pipe may soften to make it impossible to maintain the necessary strength of the stopper pipe. For example, when the temperature of the stopper pipe of copper exceeds its recrystallization temperature of 350-400.degree. C., the grain size increases. This largely attenuates the hardness of the stopper to provide an insufficient strength and hence unsatisfactory endurance thereof.
In order to overcome such an inconvenience, it can be proposed that the stopper pipe be made of a special material that does not soften when it is heated at a high temperature by soldering. In this case, however, high cost is required. Therefore, the joint pipe for conduit connection which is to be attached to the high pressure port and low pressure port must be constituted by different materials.